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Installing and Configuring SSL Support - The J2EE 1.4 Tutorial

Installing and Configuring SSL Support

What Is Secure Socket Layer Technology?

Secure Socket Layer (SSL) technology allows web browsers and web servers to communicate over a secure connection. In this secure connection, the data that is being sent is encrypted before being sent and then is decrypted upon receipt and before processing. Both the browser and the server encrypt all traffic before sending any data. SSL addresses the following important security considerations.

  • Authentication: During your initial attempt to communicate with a web server over a secure connection, that server will present your web browser with a set of credentials in the form of a server certificate. The purpose of the certificate is to verify that the site is who and what it claims to be. In some cases, the server may request a certificate that the client is who and what it claims to be (which is known as client authentication).
  • Confidentiality: When data is being passed between the client and the server on a network, third parties can view and intercept this data. SSL responses are encrypted so that the data cannot be deciphered by the third party and the data remains confidential.
  • Integrity: When data is being passed between the client and the server on a network, third parties can view and intercept this data. SSL helps guarantee that the data will not be modified in transit by that third party.

To install and configure SSL support on your stand-alone web server, you need the following components. SSL support is already provided if you are using the Application Server. If you are using a different web server, consult the documentation for your product.

To verify that SSL support is enabled, see Verifying SSL Support.

Understanding Digital Certificates

Note: Digital certificates for the Application Server have already been generated and can be found in the directory <J2EE_HOME>/domains/domain1/config/. These digital certificates are self-signed and are intended for use in a development environment; they are not intended for production purposes. For production purposes, generate your own certificates and have them signed by a CA.

To use SSL, an application server must have an associated certificate for each external interface, or IP address, that accepts secure connections. The theory behind this design is that a server should provide some kind of reasonable assurance that its owner is who you think it is, particularly before receiving any sensitive information. It may be useful to think of a certificate as a "digital driver's license" for an Internet address. It states with which company the site is associated, along with some basic contact information about the site owner or administrator.

The digital certificate is cryptographically signed by its owner and is difficult for anyone else to forge. For sites involved in e-commerce or in any other business transaction in which authentication of identity is important, a certificate can be purchased from a well-known certificate authority (CA) such as VeriSign or Thawte.

Sometimes authentication is not really a concern--for example, an administrator may simply want to ensure that data being transmitted and received by the server is private and cannot be snooped by anyone eavesdropping on the connection. In such cases, you can save the time and expense involved in obtaining a CA certificate and simply use a self-signed certificate.

SSL uses public key cryptography, which is based on key pairs. Key pairs contain one public key and one private key. If data is encrypted with one key, it can be decrypted only with the other key of the pair. This property is fundamental to establishing trust and privacy in transactions. For example, using SSL, the server computes a value and encrypts the value using its private key. The encrypted value is called a digital signature. The client decrypts the encrypted value using the server's public key and compares the value to its own computed value. If the two values match, the client can trust that the signature is authentic, because only the private key could have been used to produce such a signature.

Digital certificates are used with the HTTPS protocol to authenticate web clients. The HTTPS service of most web servers will not run unless a digital certificate has been installed. Use the procedure outlined later to set up a digital certificate that can be used by your web server to enable SSL.

One tool that can be used to set up a digital certificate is keytool, a key and certificate management utility that ships with the J2SE SDK. It enables users to administer their own public/private key pairs and associated certificates for use in self-authentication (where the user authenticates himself or herself to other users or services) or data integrity and authentication services, using digital signatures. It also allows users to cache the public keys (in the form of certificates) of their communicating peers. For a better understanding of keytool and public key cryptography, read the keytool documentation at the following URL: 

http://java.sun.com/j2se/1.5.0/docs/tooldocs/solaris/key-
tool.html

Creating a Server Certificate

A server certificate has already been created for the Application Server. The certificate can be found in the <J2EE_HOME>/domains/domain1/config/ directory. The server certificate is in keystore.jks. The cacerts.jks file contains all the trusted certificates, including client certificates.

If necessary, you can use keytool to generate certificates. The keytool stores the keys and certificates in a file termed a keystore, a repository of certificates used for identifying a client or a server. Typically, a keystore contains one client or one server's identity. The default keystore implementation implements the keystore as a file. It protects private keys by using a password.

The keystores are created in the directory from which you run keytool. This can be the directory where the application resides, or it can be a directory common to many applications. If you don't specify the keystore file name, the keystores are created in the user's home directory.

To create a server certificate follow these steps:

  1. Create the keystore.
  2. Export the certificate from the keystore.
  3. Sign the certificate.
  4. Import the certificate into a trust-store: a repository of certificates used for verifying the certificates. A trust-store typically contains more than one certificate. An example using a trust-store for SSL-based mutual authentication is discussed in Example: Client-Certificate Authentication over HTTP/SSL with JAX-RPC.

Run keytool to generate the server keystore, which we will name keystore.jks. This step uses the alias server-alias to generate a new public/private key pair and wrap the public key into a self-signed certificate inside keystore.jks. The key pair is generated using an algorithm of type RSA, with a default password of changeit. For more information on keytool options, see its online help at http://java.sun.com/j2se/1.5.0/docs/tooldocs/solaris/keytool.html.

Note: RSA is public-key encryption technology developed by RSA Data Security, Inc. The acronym stands for Rivest, Shamir, and Adelman, the inventors of the technology.

From the directory in which you want to create the keystore, run keytool with the following parameters.

  1. Generate the server certificate.

    2. <JAVA_HOME>\bin\keytool -genkey -alias server-alias
    -keyalg RSA -keypass changeit -storepass changeit
    -keystore keystore.jks

    When you press Enter, keytool prompts you to enter the server name, organizational unit, organization, locality, state, and country code. Note that you must enter the server name in response to keytool's first prompt, in which it asks for first and last names. For testing purposes, this can be localhost. The host specified in the keystore must match the host identified in the host variable specified in the <INSTALL>/j2eetutorial14/examples/common/build.properties when running the example applications.

  2. Export the generated server certificate in keystore.jks into the file server.cer.

    3. <JAVA_HOME>\bin\keytool -export -alias server-alias
    -storepass changeit -file server.cer -keystore keystore.jks

  3. If you want to have the certificate signed by a CA, read Signing Digital Certificates for more information.
  4. To create the trust-store file cacerts.jks and add the server certificate to the trust-store, run keytool from the directory where you created the keystore and server certificate. Use the following parameters:

    5. <JAVA_HOME>\bin\keytool -import -v -trustcacerts
    -alias server-alias -file server.cer
    -keystore cacerts.jks -keypass changeit
    -storepass changeit

    Information on the certificate, such as that shown next, will display.

    <INSTALL>/j2eetutorial14/examples/gs 60% keytool -import
    -v -trustcacerts -alias server-alias -file server.cer
    -keystore cacerts.jks -keypass changeit -storepass changeit
    Owner: CN=localhost, OU=Sun Micro, O=Docs, L=Santa Clara, ST=CA, C=US
    Issuer: CN=localhost, OU=Sun Micro, O=Docs, L=Santa Clara, ST=CA, C=US
    Serial number: 3e932169
    Valid from: Tue Apr 08
    Certificate fingerprints:
    MD5: 52:9F:49:68:ED:78:6F:39:87:F3:98:B3:6A:6B:0F:90
    SHA1: EE:2E:2A:A6:9E:03:9A:3A:1C:17:4A:28:5E:97:20:78:3F:
    Trust this certificate? [no]:

  5. Enter yes, and then press the Enter or Return key. The following information displays:

    6. Certificate was added to keystore
    [Saving cacerts.jks]

Signing Digital Certificates

After you've created a digital certificate, you will want to have it signed by its owner. After the digital certificate has been cryptographically signed by its owner, it is difficult for anyone else to forge. For sites involved in e-commerce or any other business transaction in which authentication of identity is important, a certificate can be purchased from a well-known certificate authority such as VeriSign or Thawte.

As mentioned earlier, if authentication is not really a concern, you can save the time and expense involved in obtaining a CA certificate and simply use the self-signed certificate.

Using a Different Server Certificate with the Application Server

Follow the steps in Creating a Server Certificate, to create your own server certificate, have it signed by a CA, and import the certificate into keystore.jks.

Make sure that when you create the certificate, you follow these rules:

  • When you press create the server certificate, keytool prompts you to enter your first and last name. In response to this prompt, you must enter the name of your server. For testing purposes, this can be localhost.
  • The server/host specified in the keystore must match the host identified in the host variable specified in the <INSTALL>/j2eetutorial14/examples/common/build.properties file for running the example applications.
  • Your key/certificate password in keystore.jks should match the password of your keystore, keystore.jks. This is a bug. If there is a mismatch, the Java SDK cannot read the certificate and you get a "tampered" message.
  • If you want to replace the existing keystore.jks, you must either change your keystore's password to the default password (changeit) or change the default password to your keystore's password:

To specify that the Application Server should use the new keystore for authentication and authorization decisions, you must set the JVM options for the Application Server so that they recognize the new keystore. To use a different keystore than the one provided for development purposes, follow these steps.

  1. Start the Application Server if you haven't already done so. Information on starting the Application Server can be found in Starting and Stopping the Application Server.
  2. Start the Admin Console. Information on starting the Admin Console can be found in Starting the Admin Console.
  3. Select Application Server in the Admin Console tree.
  4. Select the JVM Settings tab.
  5. Select the JVM Options tab.
  6. Change the following JVM options so that they point to the location and name of the new keystore. There current settings are shown below:

    7. -Djavax.net.ssl.keyStore=${com.sun.aas.instanceRoot}/config/keystore.jks
    -Djavax.net.ssl.trustStore=${com.sun.aas.instanceRoot}/config/cacerts.jks

  7. If you've changed the keystore password from its default value, you need to add the password option as well:
    -Djavax.net.ssl.keyStorePassword=your_new_password
  8. Logout of the Admin Console and restart the Application Server.

Creating a Client Certificate for Mutual Authentication

This section discusses setting up client-side authentication. When both server-side and client-side authentication are enabled, it is called mutual, or two-way, authentication. In client authentication, clients are required to submit certificates that are issued by a certificate authority that you choose to accept. From the directory where you want to create the client certificate, run keytool as outlined here. When you press Enter, keytool prompts you to enter the server name, organizational unit, organization, locality, state, and country code.

Note: You must enter the server name in response to keytool's first prompt, in which it asks for first and last names. For testing purposes, this can be localhost. The host specified in the keystore must match the host identified in the host variable specified in the <INSTALL>/j2eetutorial14/examples/common/build.properties file. If this example is to verify mutual authentication and you receive a runtime error stating that the HTTPS host name is wrong, re-create the client certificate, being sure to use the same host name that you will use when running the example. For example, if your machine name is duke, then enter duke as the certificate CN or when prompted for first and last names. When accessing the application, enter a URL that points to the same location--for example, https://duke:8181/mutualauth/hello. This is necessary because during SSL handshake, the server verifies the client certificate by comparing the certificate name and the host name from which it originates.

To create a keystore named client-keystore.jks that contains a client certificate named client.cer, follow these steps:

  1. Generate the client certificate.

    2. <JAVA_HOME>\bin\keytool -genkey -alias client-alias -keyalg RSA -keypass changeit
    -storepass changeit -keystore keystore.jks

  2. Export the generated client certificate into the file client.cer.

    3. <JAVA_HOME>\bin\keytool -export -alias client-alias
    -storepass changeit -file client.cer -keystore keystore.jks

  3. Add the certificate to the trust-store file <J2EE_HOME>/domains/domain1/config/cacerts.jks. Run keytool from the directory where you created the keystore and client certificate. Use the following parameters:

    4. <JAVA_HOME>\bin\keytool -import -v -trustcacerts
    -alias client-alias -file client.cer
    -keystore <    J2EE_HOME>/domains/domain1/config/cacerts.jks
    -keypass changeit -storepass changeit

    The keytool utility returns this message:

    Owner: CN=J2EE Client, OU=Java Web Services, O=Sun, L=Santa Clara, ST=CA, C=US
    Issuer: CN=J2EE Client, OU=Java Web Services, O=Sun, L=Santa Clara, ST=CA, C=US
    Serial number: 3e39e66a
    Valid from: Thu Jan 30 18:58:50 PST 2003 until: Wed Apr 30
    19:58:50 PDT 2003
    Certificate fingerprints:
    MD5: 5A:B0:4C:88:4E:F8:EF:E9:E5:8B:53:BD:D0:AA:8E:5A
    SHA1:90:00:36:5B:E0:A7:A2:BD:67:DB:EA:37:B9:61:3E:26:B3:89:46:
    32
    Trust this certificate? [no]: yes
    Certificate was added to keystore

For an example application that uses mutual authentication, see Example: Client-Certificate Authentication over HTTP/SSL with JAX-RPC. For information on verifying that mutual authentication is running, see Verifying That Mutual Authentication Is Running.

Miscellaneous Commands for Certificates

To check the contents of a keystore that contains a certificate with an alias server-alias, use this command:

keytool -list -keystore keystore.jks -alias server-alias -v

To check the contents of the cacerts file, use this command:

keytool -list -keystore cacerts.jks

Using SSL

An SSL connector is preconfigured for the Application Server. You do not have to configure anything. If you are working with another application server, see its documentation for setting up its SSL connector.

Verifying SSL Support

For testing purposes, and to verify that SSL support has been correctly installed, load the default introduction page with a URL that connects to the port defined in the server deployment descriptor: 

https://localhost:8181/

The https in this URL indicates that the browser should be using the SSL protocol. The localhost in this example assumes that you are running the example on your local machine as part of the development process. The 8181 in this example is the secure port that was specified where the SSL connector was created in Using SSL. If you are using a different server or port, modify this value accordingly.

The first time a user loads this application, the New Site Certificate or Security Alert dialog box displays. Select Next to move through the series of dialog boxes, and select Finish when you reach the last dialog box. The certificates will display only the first time. When you accept the certificates, subsequent hits to this site assume that you still trust the content.

Tips on Running SSL

The SSL protocol is designed to be as efficient as securely possible. However, encryption and decryption are computationally expensive processes from a performance standpoint. It is not strictly necessary to run an entire web application over SSL, and it is customary for a developer to decide which pages require a secure connection and which do not. Pages that might require a secure connection include login pages, personal information pages, shopping cart checkouts, or any pages where credit card information could possibly be transmitted. Any page within an application can be requested over a secure socket by simply prefixing the address with https: instead of http:. Any pages that absolutely require a secure connection should check the protocol type associated with the page request and take the appropriate action if https: is not specified.

Using name-based virtual hosts on a secured connection can be problematic. This is a design limitation of the SSL protocol itself. The SSL handshake, where the client browser accepts the server certificate, must occur before the HTTP request is accessed. As a result, the request information containing the virtual host name cannot be determined before authentication, and it is therefore not possible to assign multiple certificates to a single IP address. If all virtual hosts on a single IP address need to authenticate against the same certificate, the addition of multiple virtual hosts should not interfere with normal SSL operations on the server. Be aware, however, that most client browsers will compare the server's domain name against the domain name listed in the certificate, if any (this is applicable primarily to official, CA-signed certificates). If the domain names do not match, these browsers will display a warning to the client. In general, only address-based virtual hosts are commonly used with SSL in a production environment.

Enabling Mutual Authentication over SSL

This section discusses setting up client-side authentication. As mentioned earlier, when both server-side and client-side authentication are enabled, it is called mutual, or two-way, authentication. In client authentication, clients are required to submit certificates that are issued by a certificate authority that you choose to accept. If you regulate it through the application (via the Client-Certificate authentication requirement), the check is performed when the application requires client authentication. You must enter the keystore location and password in the web server configuration file to enable SSL, as discussed in Using SSL.

Here are two ways to enable mutual authentication over SSL:

  • PREFERRED: Set the method of authentication to Client-Certificate using deploytool. This enforces mutual authentication by modifying the deployment descriptor of the given application. By enabling client authentication in this way, client authentication is enabled only for a specific resource controlled by the security constraint. Setting client authentication in this way is discussed in Example: Client-Certificate Authentication over HTTP/SSL with JAX-RPC.
  • RARELY: Set the clientAuth property in the certificate realm to true. To do this, follow these steps:
    1. Start the Application Server if you haven't already done so. Information on starting the Application Server can be found in Starting and Stopping the Application Server.
    2. Start the Admin Console. Information on starting the Admin Console can be found in Starting the Admin Console.
    3. In the Admin Console tree, expand Configuration, expand Security, then expand Realms, and then select certificate. The certificate realm is used for all transfers over HTTP with SSL.
    4. Select Add to add the property of clientAuth to the server. Enter clientAuth in the Name field, and enter true in the Value field.
    5. Click Save to save these new properties.
    6. Log out of the Admin Console.

When client authentication is enabled in both of these ways, client authentication will be performed twice.

Verifying That Mutual Authentication Is Running

You can verify that mutual authentication is working by obtaining debug messages. This should be done at the client end, and this example shows how to pass a system property in targets.xml so that targets.xml forks a client with javax.net.debug in its system properties, which could be added in a file such as <INSTALL>/j2eetutorial14/examples/security/common/targets.xml.

To enable debug messages for SSL mutual authentication, pass the system property javax.net.debug=ssl,handshake, which will provide information on whether or not mutual authentication is working. The following example modifies the run-mutualauth-client target from the <INSTALL>/j2eetutorial14/examples/security/common/targets.xml file by adding sysproperty as shown in bold: 

<target name="run-mutualauth-client" 
description="Runs a client with mutual authentication over 
SSL">
  <java classname="${client.class}" fork="yes" >
    <arg line="${key.store} ${key.store.password} 
          ${trust.store} ${trust.store.password} 
          ${endpoint.address}" />
    <sysproperty key="javax.net.debug" value="ssl, 
          handshake" />
    <sysproperty key="javax.net.ssl.keyStore"
          value="${key.store}" />
    <sysproperty key="java.net.ssl.keyStorePassword"
          value="${key.store.password}"/>
    <classpath refid="run.classpath" />
  </java>
</target>